Heterocyclic chromenes and their use in the field of ophthalmic optics

ABSTRACT

The invention relates to photochromic compounds of general formula: ##STR1## wherein R a , R b  and R c  is denote hydrogen; alkyl; aryl; OR, SR, COR or COOR, in which R denotes hydrogen, alkyl or aryl, amino of formula NR 1  R 2  in which R 1  and R 2  denote hydrogen, alkyl, cycloalkyl or an aryl; a halogen atom; a mono- or polyhaloalkyl group; or an NO 2 , CN or SCN group; n and m denote integers from 1 to 5; p is equal to 1 or 2; and H is a 5-members aromatic heterocycle containing one or more heteroatoms selected from nitrogen, oxygen and sulfur, these heterocyclic nuclei being eventually substituted by one or more alkyl, alkoxy, amino, aryl or aralkyl groups or condensed with a phenyl nucleus, a substituted phenyl nucleus or a 6-members cycloaliphatic nucleus and to their use in ophtalmic optics.

The present application is a continuing application of U.S. patentapplication Ser. No. 08/625,727, filed Mar. 29, 1996, now U.S. Pat. No.5,631,720, which is a continuing application of U.S. patent applicationSer. No. 08/033, 893, filed Mar. 19, 1993, now issued as U.S. Pat. No.5,527,911, from which priority is claimed.

The subject of the invention is novel photochromic compounds, moreparticularly, photochromic compounds containing in their chemicalformula, a nucleus of the chromene or benzopyran family, and their usein the field of ophthalmic optics, in particular in and/or on ophthalmiclenses.

Photochromism is a phenomenon which has been known for many years. Acompound is said to be photochromic when this compound changes color onirradiation with a light beam, some of whose wavelengths are situated inthe ultraviolet region, and returns to its original color as soon as theirradiation ceases.

The applications of this phenomenon are numerous, but one of the knownapplications which is particularly advantageous, relates to the field ofophthalmic optics.

Such compounds can be used in the manufacture of spectacle lenses orglasses, for the purpose of screening out light radiation according toits intensity.

The incorporation of photochromic compounds in an organic materialconstituting an ophthalmic lens makes it possible to obtain a glasswhose weight is greatly reduced compared with conventional lenses madefrom mineral glass, which contain silver halides by way of photochromicagent. Their incorporation in organic materials has always posedtechnical difficulties.

However, all compounds exhibiting photochromic properties are notnecessarily usable in the field of ophthalmic optics. Indeed, thephotochromic compound should meet a certain number of criteria,including among others:

a high colorability which is a measure of the capacity of a photochromiccompound to exhibit an intense color after isomerization;

a coloration after absorption of light which makes the photochromiccompound, alone or in combination with other photochromic compounds,capable of being used in ophthalmic glasses or lenses;

an absence of coloration or very weak coloration in the initial form;

a rapid coloration or decolorization kinetics;

a photochromism which manifests itself within the widest possibletemperature range, and in particular, preferably between 0° and 40° C.

The known organic photochromic compounds currently used generallyexhibit a decreasing photochromism when the temperature increases, suchthat the photochromism is particularly pronounced at temperatures closeto 0° C., whereas it is much fainter or even absent at temperatures ofthe order of 40° C. which are temperatures that can be achieved inglasses especially during exposure to sunlight.

Another problem encountered by the photochromic compounds of the stateof the art is their lifetime. A relatively reduced lifetime is indeedobserved for some products of the state of the art. Indeed, after acertain number of coloration and decolorization cycles, the photochromiccompound generally gets stuck in an open and colored form and no longerexhibits reversible photochromic properties.

Many chromene type photochromic compounds have been synthesized byProfessor HELLER in, for example, Patent Application EP 246,114 whichdescribes a series of photochromic compounds in which a spiroadamantanegroup is introduced in position 2 of the benzopyran or naphtho-pyrannucleus, or even Patent Application WO 90/07507 where 2 cyclopropylgroups are attached in position 2 of the cyclic benzopyran ornaphthopyran compound. Patent Application WO 91/00861 by the sameinventor can also be mentioned, in which a norcamphor group or atricyclo-decane group is introduced in position 2 of photochromiccompounds of the same type.

Benzopyran and naphthopyran type photochromic derivatives, substitutedin position 2 of the pyran ring have already been described in U.S. Pat.No. 3,567,605. However, these compounds possess relatively lowdecolorization kinetic constants.

Moreover, photochromic derivatives also possessing low decolorizationkinetic constants and less suitable for the application envisaged, arealso known from Application EP-A-0,401,958.

The Applicant Company has discovered a novel family of benzopyranspossessing particularly advantageous photochromic properties. Thecompounds conforming to the invention indeed possess a highcolorability, in particular in the red region, which is particularlyuseful in ophthalmic optics, it then being possible for these compoundsto be used with photochromic compounds producing a blue color, so as toobtain a final natural coloration during exposure to light.

The compounds conforming to the invention possess, moreover, an absenceof coloration or a very weak coloration in the initial state, and arapid coloration and decolorization kinetics within a very widetemperature range, in particular between 0° and 40° C.

The Applicant also observed that these compounds possessed aparticularly long lifetime.

The consequence of all these properties is that these novel photochromiccompounds are particularly advantageous with respect to their use inophthalmic optics and in particular to their use in and/or on ophthalmiclenses.

Within the context of the invention, ophthalmic lenses refer tospectacle glasses, in particular sunglasses and contact lenses.

One subject of the invention therefore consists of novel photochromiccompounds.

Another subject of the invention consists of their use in ophthalmicoptics.

The subject of the invention is also compositions intended to be usedfor coating ophthalmic lenses or their incorporation in these lenses.

Other subjects of the invention will emerge on reading the followingdescription and examples.

The photochromic compound conforming to the invention is essentially ofthe general formula: ##STR2## in which R^(a), R^(b) and R^(c) denote,independently of each other, a hydrogen atom; an alkyl group; an arylgroup; an OR, SR, COR or COOR group, in which R denotes a hydrogen atom,an alkyl group or an aryl group; an amino group of formula NR₁ R₂ inwhich R₁ and R₂ denote, independently of each other, a hydrogen atom, analkyl group, a cycloalkyl group, an aryl group, R₁ and R₂ being capableof forming with the nitrogen atom, a heterocycle containing 4 to 7members and being capable of containing, in addition, one or moreheteroatoms chosen from nitrogen, oxygen, sulfur, a halogen atom; amono- or polyhaloalkyl group; an NO₂, CN or SCN group; n and m denoteintegers from 1 to 5 depending on the number of substitutions on thenucleus and p may be equal to 1 or 2 depending on the number ofsubstitutions on the nucleus. The radicals R^(a), R^(b) and R^(c) mayhave different meanings when m, n and p are greater than 1 and dependingon the position on the nuclei; H is an aromatic heterocycle having 4 to7 members and preferably 5 or 6 members containing one or moreheteroatoms chosen from nitrogen, oxygen, sulfur, these heterocyclicnuclei being capable of being substituted by one or more alkyl, alkoxy,amino, aryl or aralkyl groups or condensed with an aromatic nucleus.

In the abovementioned formula, an alkyl group preferably denotes a grouphaving 1 to 6 carbon atoms, a cycloalkyl group preferably denotes agroup having 3 to 7 carbon atoms, the aryl group preferably denotes aphenyl group, halogen preferably denotes chlorine, bromine, fluorine,the polyhaloalkyl group preferably denotes a CF₃ group.

The heterocyclic nucleus is represented more particularly by the formula(II): ##STR3## in which:

Y denotes CR₅ R₆ in which R₅ and R₆ denote, independently of each other,hydrogen, C₁ -C₆ alkyl, phenyl; CR₅, R₅ having the meaning given above,the carbon atom being linked to one of the neighboring atoms by a doublebond; NR₇ in which R₇ denotes hydrogen, C_(1-C) ₆ alkyl or N-- linked tothe neighboring atom by a double bond; oxygen or sulfur; r being equalto 0 or 1;

X and Z denote, independently of each other, CR₈ R₉, in which R₈ and R₉denote, independently of each other, hydrogen, C₁ -C₆ alkyl, phenyl;CR₈ - R₈ having the meaning given above and the carbon atom being linkedto the neighboring atom by a double bond; NR₁₀ where R₁₀ denoteshydrogen or C₁ -C₆ alkyl or alternatively N-- linked to the neighboringatom by a double bond; oxygen, sulfur, s or t is equal to 0 or 1 and thesum r+s+t is not less than 2 and at least one of the groups Y, X, Zdenotes NH--, --N--; --O-- or --S, the meanings --N--, --O--, --S--being preferred;

R₃ and R₄ denote, independently of each other, hydrogen, C₁ -C₆ alkyl,phenyl, u is equal to 0 or 1 and the carbon atom forming with one of theneighboring carbon atoms, a double bond when u is equal to O, R₃ and Xor R₄ and Z being capable of forming together elements of a ring having5 or 6 members which are aromatic or non-aromatic, preferably benzene,or a naphthalene nucleus optionally substituted by a (R₁₁)_(v) group,R₁₁ having the meaning of any one of the groups R^(a), R^(b) and R^(c),as defined above and v being an integer from 0 to 4 in the case of abenzene ring or from 0 to 6 in the case of a naphthalene ring.

The heterocyclic nuclei particularly preferred are chosen from thegroups of formula (II), in which r is equal to O, X denotes O, S or N, Zdenotes CR₈ R₉ or X denotes CR₈ R₉ and Z denotes O, S or N and R₃, R₄,R₈, R₉ have the meanings given above, and when Z or alternatively Xdenotes CR₈, R₄ and R₈ or alternatively R₃ and R₈ may together form anoptionally substituted benzene ring; X preferably denotes O or S.

Other preferred compounds are those for which r+s+t=3, and at least oneof the groups X, Y or Z denotes N, at least one of these groups denotingCR₈ R₉ or CR₈ ; Z preferably denotes N, X or Y denote N and the otherCR₈, R₈, R₉ having the meanings given above.

The heterocyclic nuclei more particularly preferred are chosen frompyrimidine, pyrazine, furan nuclei, optionally condensed with anaromatic nucleus to form an optionally substituted benzofuran, thiazolering.

The families of compounds more particularly preferred are of theformulae: ##STR4## in which R^(a), R^(b), R^(c), R₁₁ and n, m, p and vhave the meanings given above, X₁ meaning oxygen or sulfur andpreferably oxygen, R₁₂ having the meaning given for R₁₁ and w being aninteger from 0 to 2.

The compounds conforming to the invention may be prepared according tothe following reaction scheme: ##STR5##

In these formulae, H denotes a heterocyclic group having the meaninggiven above. The phenyl groups may be substituted by a group R^(a) orR^(b) as defined above.

The photochromic compounds conforming to the invention may be used forproducing photochromic ophthalmic lenses.

The compounds conforming to the invention may be introduced into acomposition intended to be applied on or to be introduced into atransparent organic polymer material to give a transparent photochromicarticle. They may also be introduced into solid compositions such asplastic films, patches and lenses for producing materials which can beused especially as ophthalmic lenses, sunglasses, viewfinders, cameraoptics and screening agents.

The liquid compositions which constitute a subject of the inventionessentially contain, in dissolved or dispersed form, the compoundsconforming to the invention in a medium based on solvents suitable forapplying to or introducing into a transparent polymer material.

Solvents which can be more particularly used are organic solvents chosenfrom benzene, toluene, chloroform, ethyl acetate, methyl ethyl ketone,acetone, ethyl alcohol, methyl alcohol, acetonitrile, tetrahydrofuran,dioxane, ethylene glycol methyl ether, dimethylformamide, dimethylsulfoxide, methyl cellosolve, morpholine and ethylene glycol.

When the compounds conforming to the invention are dispersed, the mediummay also contain water.

According to another embodiment, the compounds conforming to theinvention may be introduced and preferably dissolved in colorless ortransparent solutions prepared from polymers, copolymers or mixtures ofpolymers which are transparent in a suitable organic solvent.

Examples of such solutions are among others, solutions of nitrocellulosein acetonitrile, polyvinyl acetate in acetone, polyvinyl chloride inmethyl ethyl ketone, polymethyl methacrylate in acetone, celluloseacetate in dimethylformamide, polyvinylpyrrolidone in acetonitrile,polystyrene in benzene, ethyl cellulose in methylene chloride.

These compositions may be applied on transparent supports such as inpolyethylene glycol terephthalate, borylated paper, cellulosetriacetate, and dried to give a photochromic material which can becomecolored in the presence of ultraviolet radiation and which returns toits noncolored and transparent state in the absence of the radiationsource.

The photochromic compounds of the present invention or the above definedcompositions containing them, may be applied or incorporated in a solidtransparent polymerized organic material suitable for ophthalmicelements such as ophthalmic lenses or materials useful for use insunglasses, viewfinders, camera optics and screening agents.

The following may be mentioned as transparent solid materials which maybe used to produce ophthalmic lenses conforming to the invention:polyol(allyl carbonate), polyacrylate, poly(alkyl acrylate) polymerssuch as polymethyl methacrylates, cellulose acetate, cellulosetriacetate, cellulose propionate acetate, cellulose butyrate acetate,poly(vinyl acetate), poly(vinyl alcohol), polyurethanes, polycarbonates,polyethylene terephthalates, polystyrenes, (polystyrene methylmethacrylates), styrene and acrylonitrile copolymers, polyvinylbutyrates.

Transparent copolymers or mixtures of transparent copolymers are alsosuitable for producing such materials.

In this respect, there may be mentioned materials prepared frompolycarbonates such as poly 2,2-(4,4'-dioxydiphenol)propane!, polymethylmethacrylate, polyol-(allyl carbonate) such as in particular diethyleneglycol bis(allyl carbonate) and its copolymers such as for example withvinyl acetate. There may be mentioned in particular the copolymers ofdiethylene glycol bis(allyl carbonate) and vinyl acetate (80-90/10-20)and even the copolymer of diethylene glycol bis(allyl carbonate) withvinyl acetate, cellulose acetate and cellulose propionate, cellulosebutyrate (80-85/15-20).

The polyols(allyl carbonate) are prepared using allyl carbonates oflinear or branched, aliphatic or aromatic liquid polyols such as thealiphatic glycols of bis(allyl carbonate) or alkylene bis(allylcarbonates). Among the polyol(allyl carbonates) which may be used forpreparing the transparent solid materials which may be used inaccordance with the invention, there may be mentioned ethylene glycolbis(allyl carbonate), diethylene glycol bis (2-methylallylcarbonate),diethylene glycol bis(allyl carbonate), ethylene glycolbis(2-chloroallyl-carbonate), triethylene glycol bis(allyl carbonate),1,3-propanediol bis(allyl carbonate), propylene glycolbis(2-ethylallylcarbonate), 1,3-butanediol bis(allyl carbonate),1,4-butanediol bis(2-bromoallylcarbonate), dipropylene glycol bis(allylcarbonate), trimethylene glycol bis(2-ethylallylcarbonate),pentamethylene glycol bis(allyl carbonate), isopropylene bisphenolbis(allyl carbonate). The most important product consists of diethyleneglycol bis(allyl carbonate) also known under the name CR39.

The amount of photochromic compounds to be used in conformity with theinvention, either in the composition or at the time of its introductioninto the solid support, is not critical and generally depends on theintensity of the color which the composition can confer on the materialafter exposure to radiation. Generally, the greater the amount ofphotochromic compounds added, the more intense the coloration will beunder irradiation.

In conformity with the invention, a sufficient amount is used to conferon the treated material the property of changing color on exposure toradiation. This amount of photochromic compounds is generally between0.01 and 20% by weight, and preferably between 0.05 and 10% by weightrelative to the total weight of the optic material or composition.

The photochromic compounds conforming to the invention may also beintroduced into a temporary transfer carrier (such as a varnish forminga coating on a substrate) and be subsequently thermally transferred inthe substrate as described in particular in U.S. Pat. No. 4,286,957 orU.S. Pat. No. 4,880,667.

These compounds may be used with other photochromic compounds such asphotochromic compounds giving rise to various colorations such as blueand green, which are known in the state of the art. Accordingly,spiro(indoline-oxazines), which are well known in the state of the art,may be used.

Once applied to the ophthalmic materials or introduced into suchmaterials, the appearance of a coloration is observed after exposure toUV radiation, and there is a return to the original color ortransparency when the exposure to UV radiation is discontinued.

The compounds conforming to the invention have the advantage ofpermitting this change in coloration many times and this at temperatureswhich vary widely between 0° and 40° C.

The following examples are intended to illustrate the invention without,however, being of a restrictive nature.

EXAMPLE 1 ##STR6##

2.09 g of 6-hydroxyquinazoline (1.43×10⁻² mole) are dissolved in 10 mlof anhydrous toluene and placed under an inert atmosphere.

A stoichiometric toluene solution of ortho-titanate is added. Thereaction mixture is then refluxed for 1 hour. The heating is thencontinued so as to remove the ethanol thus formed. After reequilibratingto room temperature, 1.46 g (7.01×10⁻³ mole) of β-phenylcinnam- aldehydeare added. The reflux is then continued for 2 hours under an inertatmosphere. After reequilibrating to room temperature, the reactionmixture is extracted using a 2M solution of ammonium chloride and thenextracted three times using a 2M solution of sodium hydroxide.

The mixture is dried over MgSO₄. The solvent is removed using a rotaryevaporator. 50 ml of hexane are added. The precipitate is recovered andrecrystallized from cyclohexane (white solid).

melting point=162° C.

Yield=43%.

When a toluene solution of the compound of Example 1 is irradiated withUV radiation, the solution becomes red (438 nm), when the ultravioletradiation is stopped, the solution becomes colorless again.

EXAMPLE 2 ##STR7##

a) 2-Hydroxydibenzofuran (1.842 g, 10⁻² mole) is dissolved in anhydroustoluene. A stoichiometric toluene solution of ortho-titanate is added.The reaction mixture is refluxed for 30 minutes and then the ethanolthus formed is distilled off.

b) After reequilibrating to room temperature, a toluene solution ofβ-phenylcinnamaldehyde (1.041 g, 5×10⁻³ mole) is slowly added. Thereflux is continued under an inert atmosphere for 1 h 30 minutes.

After reequilibrating to room temperature, the solvent is removed usinga rotary evaporator. Dichloro-methane and a 2N solution of sodiumhydroxide are then added.

The mixture is extracted continuously for 24 hours. It is dried overMgSO₄. The solvent is removed using a rotary evaporator.

The chromene obtained is purified by flash chromatography (100%pentane). It is recrystallized from cyclohexane (yellow solid).

melting point=134° C.

Yield=40%.

When a toluene solution of Example 2 is irradiated with UV radiation,the solution becomes red (505 nm), when the ultraviolet radiation isstopped, the solution becomes colorless again.

EXAMPLE 3 ##STR8##

Stage 1 : Synthesis of 6-hydroxy-2,3-diphenylquinoxaline

a) 6-Methoxy-2,3-diphenylquinoxaline ##STR9##

2 g of 4-methoxy-1,2-phenylenediamine dihydrochloride (1.15×10⁻² mole)are dissolved in 20 ml of anhydrous ethanol under an inert atmosphere.

A stoichiometric ethanolic solution of triethylamine is added. Thestirring is continued at room temperature for 30 minutes. An ethanolicsolution of benzil (2.46 g, 1.17×10⁻² mole) is added. The reactionmixture is refluxed for 4 hours. The precipitate formed is recovered byfiltration. It is dried under vacuum to obtain 2.4 g of the desiredcompound.

melting point=152° C.

Yield=70%.

b) 6-Hydroxy-2,3-diphenylquinoxaline ##STR10##

A mixture of 6-methoxy-2,3-diphenylquinoxaline (1 g; 3.2×10⁻³ mole) and10 ml of HBr (48%) is heated at 120° C. for 9 hours. Afterreequilibrating to room temperature, the solution is neutralized (pH :7.5) with a 1M solution of NH₄ OH.

The precipitate formed is recovered by filtration and purified by flashchromatography (99% CHCl₃, 1% CH₃ OH). The solvent is removed using arotary evaporator.

melting point=251° C.

Yield=43%.

Stage 2

a) 6-Hydroxy-2,3-diphenylquinoxaline (1 g, 3.37×10⁻³ mole) is dissolvedin anhydrous toluene. A stoichiometric toluene solution ofortho-titanate is added. The reaction mixture is refluxed for 30 minutesand then the ethanol thus formed is distilled off.

b) After reequilibrating to room temperature, a toluene solution ofp-phenylcinnamaldehyde (0.33 g, 1.58×10⁻³ mole) is slowly added. Themixture is refluxed under an inert atmosphere for 2 hours.

After reequilibrating to room temperature, the reaction mixture isextracted with a 2M solution of ammonium chloride, and then three timeswith a 2M solution of sodium hydroxide. It is dried over MgSO₄. Thesolvent is removed using a rotary evaporator. 25 ml of cyclohexane areadded. A precipitate is recovered and purified by chromatography (100%ether). It is recrystallized from cyclohexane (white solid).

melting point=159° C.

Yield=10%

EXAMPLE 4 ##STR11##

Stage 1: Synthesis of 6-hydroxy-2-methylbenzothiazole

1 g of commercial 6-methoxy-2-methylbenzothiazole (5.5×10⁻³ mole) ismixed with 0.9 g of azeotropic hydrobromic acid at 48% (1.1×10⁻² mole).The reaction is carried out in a sealed tube at 125° C. for 6 hours.

After neutralizing the solution with 3N ammonium hydroxide (pH=7), thehydroxylated compound is extracted with chloroform. The yield isquantitative. (Synthesis described in French Patent FR-2,647,790).

melting point=147° C.

Stage 2 :

0.965 g of 6-hydroxy-2-methylbenzothiazole (5.83×10⁻³ mole) is dissolvedin 10 ml of anhydrous toluene and placed under an inert atmosphere.

A stoichiometric toluene solution of ortho-titanate is added. Thereaction mixture is then refluxed for 30 minutes. The heating is thencontinued so as to remove the ethanol thus formed. After reequilibratingto room temperature, 0.585 g (2.8×10⁻³ mole) of β-phenylcinnamaldehydeis added. The reflux is continued for 1 h 30 minutes under an inertatmosphere. After reequilibrating to room temperature, the reactionmixture is extracted with a 2M solution of ammonium chloride, and thenthree times with a 2M solution of sodium hydroxide.

The mixture is dried over MgSO₄. The solvent is removed using a rotaryevaporator. 50 ml of hexane are added. The precipitate is recovered andrecrystallized from cyclohexane (yellow solid).

melting point=215° C. Yield=35%

                  TABLE 1                                                         ______________________________________                                        Spectrokinetic parameters in toluene at 25° C., at a                   concentration of 2.5 × 10.sup.-5 M                                                                  Kinetic constant                                          Color of            of thermal                                                                              A.sub.o                                         photo-    λ.sub.max                                                                        decolorization                                                                          (color-                                 Example merocyanine                                                                             (nm)      K in s.sup.-1                                                                           ability)                                ______________________________________                                        1       Red       438       0.47      1.03                                    2       Red       505       0.23      0.41                                    3       Red       471       0.1       0.93                                    4       Red       430-508   0.25      0.14                                    ______________________________________                                    

EXAMPLE 5 ##STR12##

a) 3 g of 6-quinolinol (2.07×10⁻² mole) are dissolved in anhydroustoluene. A stoichiometric solution of ortho-titanate (4.722 g,equivalent to 2.07×10⁻² mole of ortho-titanate) is added. The mixture isrefluxed for 1 hour and then the ethanol formed is distilled off.

b) a toluene solution of β-phenylcinnamaldehyde (2.047 g, 9.83×10⁻³mole) is then slowly added.

After reequilibrating to room temperature, the mixture is washed with asolution of ammonium chloride, and then with a 2M solution of sodiumhydroxide.

The aqueous phase is dried over MgSO₄ and the solvent is removed underreduced pressure.

The product is purified by flash chromatography (80% pentane, 20% Et₂O). It is recrystallized from a xylene-heptane mixture.

Melting point=222° C.

Yield 62%.

EXAMPLE 6 ##STR13##

1.832 g (10 mmol) of 2-hydroxycarbazole are dissolved in 50 ml ofanhydrous toluene and placed under an inert atmosphere.

A toluene solution (10 ml) of 2.28 g of ortho-titanate (10 mmol) isgradually added.

The reaction mixture is heated at the reflux temperature of toluene for40 minutes and the ethanol is simultaneously distilled off.

The mixture is allowed to reequilibriate to room temperature beforeadding a toluene solution (35 ml) of 1 g of β-phenylcinnamaldehyde (4.8mmol). When the addition is complete, the mixture is refluxed for 2hours. The solvent is removed under reduced pressure.

The product is rinsed with a 2M solution of NH₄ Cl and then with a 2Msolution of NaOH. A large quantity of emulsion then appears which istaken up in chloroform. The solution is allowed to settle.

The aqueous phase is filtered after adjusting the pH to 8.5. The alcoholis recovered.

The solvent of the organic phase is removed under reduced pressure. Theresidue precipitates from hexane. It is filtered. The product obtainedis purified by flash chromatography, using a pentane/ether mixture(75/25) as eluent.

Mass obtained=0.3 g

Molecular weight (g. mol.)=375.5

Melting point 182° C.

Yield =17%

                  TABLE 2                                                         ______________________________________                                        Spectrokinetic parameters in toluene at 25° C.,                        at a concentration of 2.5 × 10.sup.-5 M                                                             Kinetic constant                                          Color of            of thermal                                                                              A.sub.o                                         photo-    λ.sub.max                                                                        decolorization                                                                          (color_                                 Examples                                                                              merocyanine                                                                             (nm)      K in s.sup.-1                                                                           ability)                                ______________________________________                                        5       Orange    436       0.13      0.61                                    6       Red       436       0.15      0.99                                    ______________________________________                                    

EXAMPLE 7 ##STR14##

0.77 g of 5-hydroxyindole (5.77×10⁻³ mole) is dissolved in 10 ml ofanhydrous toluene and placed under an inert atmosphere.

A stoichiometric toluene solution of ortho-titanate is added. Thereaction mixture is then refluxed for 40 minutes. The heating is thencontinued so as to remove the ethanol thus formed. After reequilibratingto room temperature, 0.55 g (2.66×10⁻³ mole) of β-phenylcinnamaldehydeis added. The reflux is then continued for 1 hour 30 minutes under aninert atmosphere. After reequilibrating to room temperature, thereaction mixture is extracted with a 2M solution of ammonium chloride,and then three times with a 2M solution of sodium hydroxide.

The mixture is dried over MgSO₄. The solvent is removed using a rotaryevaporator. It is purified by chromatography on silica (100% toluene). Ared oil is recovered and crystallized from pentane.

melting point=143° C.

Yield=33%.

EXAMPLE 8 ##STR15##

2.16 g (1.146×10⁻² mole) of 2-hydroxy-5,6,7,8-tetrahydrodibenzofuran aredissolved in 10 cm³ of toluene, and then a stoichiometric solution ofortho-titanate (2.614 g, 1.146×10⁻² mole) is added.

The mixture is refluxed for 1 hour and then the ethanol formed isdistilled off.

The mixture is reequilibriated to room temperature.

A toluene solution containing 1.313 g, equivalent to 6.3×10⁻³ mole ofβ-phenylcinnamaldehyde, is then added.

The mixture is refluxed for 3 h 30 minutes.

After reequilibriating to room temperature, the reaction medium isextracted with 2M sodium hydroxide.

The mixture is dried over MgSO₄ and the solvent is removed.

The product is purified by flash chromatography (85% hexane, 19% Et₂ O).It is recrystallised from a benzene-heptane mixture.

Melting point=187° C.

Yield=10%.

We claim:
 1. A photochromic compound which is of the original formula:##STR16## wherein R^(a), R^(b) and R^(c) are independently of eachother, a hydrogen atom, an alkyl group, an aryl group, an OR, SR, COR orCOOR group, where R denotes a hydrogen atom, an alkyl group or an arylgroup, an amino group of formula NR₁ R₂ where R₁ and R₂ denote,independently of each other, a hydrogen atom, an alkyl group, acycloalkyl group or an aryl group; a halogen atom; a mono- orpolyhaloalkyl group; or an NO₂, CN or SON group; n and m denote integersfrom 1 to 5; p is equal to 1 or 2; R^(a), R^(b) and R^(c) may havedifferent meanings when m, n and p are greater than 1; and H is a5-members aromatic heterocycle of the general formula: ##STR17## inwhich: X or Z represents --N-- or --NH--, and the remaining one of X orZ represents S, O or a CR₈ radical in which R₈ is hydrogen, C₁ --C₆alkyl or phenyl, the carbon atom being linked to the neighboring atom bya double bond; andR₄ is hydrogen, C₁ -C₆ alkyl, phenyl or when X or Z is--NH--, may form with the remaining one of X or Z a phenyl ring, or asubstituted phenyl ring.
 2. The compound of claim 1 comprising compoundsof a formula: ##STR18##
 3. An ophthalmic lens comprising a transparentorganic polymer material and at least one photochromic compound asdefined in claim 1, in an amount sufficient to enable a said ophthalmiclens to change color upon exposure to ultraviolet radiation.
 4. Theophthalmic lens of claim 3, wherein said at least one photochromiccompound is in the form of a coating on said transparent organic polymermaterial.
 5. The ophthalmic lens of claim 3, wherein said at least onephotochromic compound is incorporated within said transparent organicpolymer material.
 6. The ophthalmic lens of claim 5, which contains 0.01to 20% by weight of photochromic compounds.
 7. The ophthalmic lens ofclaim 5, which contains 0.05 to 10% by weight of photochromic compounds.8. The ophthalmic lens of claim 3, wherein said transparent organicpolymer material is selected from the group consisting ofpolyol(allylcarbonate), polyacrylate, poly(alkylacrylate) polymers,cellulose acetate, cellulose triacetate, cellulose propionate acetate,cellulose butyrate acetate, poly(vinylacetate), poly(vinyl alcohol),polyurethanes, polycarbonates, poly(ethylene terephthalates),polystyrenes, poly(styrene methylmethacrylates), styrene andacrylonitrile copolymers, and polyvinylbutyrates.
 9. The ophthalmic lensof claim 3, wherein said transparent organic polymer material isselected from the group consisting of poly2,2-(4,4'-dioxydiphenol)propane!, poly(methylmethacrylate) andpolyol(allyl-carbonates).